grep, egrep, fgrep - print lines matching a pattern
SYNOPSIS
grep [options] PATTERN [FILE...]
grep [options] [-e PATTERN | -f FILE] [FILE...]
DESCRIPTION
Grep searches the named input FILEs (or standard input if
no files are named, or the file name - is given) for lines
containing a match to the given PATTERN. By default, grep
prints the matching lines.
In addition, two variant programs egrep and fgrep are
available. Egrep is the same as grep -E. Fgrep is the
same as grep -F.
OPTIONS
-A NUM, --after-context=NUM
Print NUM lines of trailing context after matching
lines.
-a, --text
Process a binary file as if it were text; this is
equivalent to the --binary-files=text option.
-B NUM, --before-context=NUM
Print NUM lines of leading context before matching
lines.
-C [NUM], -NUM, --context[=NUM]
Print NUM lines (default 2) of output context.
-b, --byte-offset
Print the byte offset within the input file before
each line of output.
--binary-files=TYPE
If the first few bytes of a file indicate that the
file contains binary data, assume that the file is
of type TYPE. By default, TYPE is binary, and grep
normally outputs either a one-line message saying
that a binary file matches, or no message if there
is no match. If TYPE is without-match, grep
assumes that a binary file does not match; this is
equivalent to the -I option. If TYPE is text, grep
processes a binary file as if it were text; this is
equivalent to the -a option. Warning: grep
--binary-files=text might output binary garbage,
which can have nasty side effects if the output is
a terminal and if the terminal driver interprets
some of it as commands.
Suppress normal output; instead print a count of
matching lines for each input file. With the -v,
--invert-match option (see below), count non-match
ing lines.
-d ACTION, --directories=ACTION
If an input file is a directory, use ACTION to pro
cess it. By default, ACTION is read, which means
that directories are read just as if they were
ordinary files. If ACTION is skip, directories are
silently skipped. If ACTION is recurse, grep reads
all files under each directory, recursively; this
is equivalent to the -r option.
-E, --extended-regexp
Interpret PATTERN as an extended regular expression
(see below).
-e PATTERN, --regexp=PATTERN
Use PATTERN as the pattern; useful to protect pat
terns beginning with -.
-F, --fixed-strings
Interpret PATTERN as a list of fixed strings, sepa
rated by newlines, any of which is to be matched.
-f FILE, --file=FILE
Obtain patterns from FILE, one per line. The empty
file contains zero patterns, and therefore matches
nothing.
-G, --basic-regexp
Interpret PATTERN as a basic regular expression
(see below). This is the default.
-H, --with-filename
Print the filename for each match.
-h, --no-filename
Suppress the prefixing of filenames on output when
multiple files are searched.
--help Output a brief help message.
-I Process a binary file as if it did not contain
matching data; this is equivalent to the --binary-
files=without-match option.
-i, --ignore-case
Ignore case distinctions in both the PATTERN and
the input files.
Suppress normal output; instead print the name of
each input file from which no output would normally
have been printed. The scanning will stop on the
first match.
-l, --files-with-matches
Suppress normal output; instead print the name of
each input file from which output would normally
have been printed. The scanning will stop on the
first match.
--mmap If possible, use the mmap(2) system call to read
input, instead of the default read(2) system call.
In some situations, --mmap yields better perfor
mance. However, --mmap can cause undefined behav
ior (including core dumps) if an input file shrinks
while grep is operating, or if an I/O error occurs.
-n, --line-number
Prefix each line of output with the line number
within its input file.
-q, --quiet, --silent
Quiet; suppress normal output. The scanning will
stop on the first match. Also see the -s or --no-
messages option below.
-r, --recursive
Read all files under each directory, recursively;
this is equivalent to the -d recurse option.
-s, --no-messages
Suppress error messages about nonexistent or
unreadable files. Portability note: unlike GNU
grep, traditional grep did not conform to POSIX.2,
because traditional grep lacked a -q option and its
-s option behaved like GNU grep's -q option. Shell
scripts intended to be portable to traditional grep
should avoid both -q and -s and should redirect
output to /dev/null instead.
-U, --binary
Treat the file(s) as binary. By default, under MS-
DOS and MS-Windows, grep guesses the file type by
looking at the contents of the first 32KB read from
the file. If grep decides the file is a text file,
it strips the CR characters from the original file
contents (to make regular expressions with ^ and $
work correctly). Specifying -U overrules this
guesswork, causing all files to be read and passed
to the matching mechanism verbatim; if the file is
a text file with CR/LF pairs at the end of each
line, this will cause some regular expressions to
than MS-DOS and MS-Windows.
-u, --unix-byte-offsets
Report Unix-style byte offsets. This switch causes
grep to report byte offsets as if the file were
Unix-style text file, i.e. with CR characters
stripped off. This will produce results identical
to running grep on a Unix machine. This option has
no effect unless -b option is also used; it has no
effect on platforms other than MS-DOS and MS-Win
dows.
-V, --version
Print the version number of grep to standard error.
This version number should be included in all bug
reports (see below).
-v, --invert-match
Invert the sense of matching, to select non-match
ing lines.
-w, --word-regexp
Select only those lines containing matches that
form whole words. The test is that the matching
substring must either be at the beginning of the
line, or preceded by a non-word constituent charac
ter. Similarly, it must be either at the end of
the line or followed by a non-word constituent
character. Word-constituent characters are let
ters, digits, and the underscore.
-x, --line-regexp
Select only those matches that exactly match the
whole line.
-y Obsolete synonym for -i.
-Z, --null
Output a zero byte (the ASCII NUL character)
instead of the character that normally follows a
file name. For example, grep -lZ outputs a zero
byte after each file name instead of the usual new
line. This option makes the output unambiguous,
even in the presence of file names containing
unusual characters like newlines. This option can
be used with commands like find -print0, perl -0,
sort -z, and xargs -0 to process arbitrary file
names, even those that contain newline characters.
REGULAR EXPRESSIONS
A regular expression is a pattern that describes a set of
strings. Regular expressions are constructed analogously
to arithmetic expressions, by using various operators to
Grep understands two different versions of regular expres
sion syntax: "basic" and "extended." In GNU grep, there
is no difference in available functionality using either
syntax. In other implementations, basic regular expres
sions are less powerful. The following description
applies to extended regular expressions; differences for
basic regular expressions are summarized afterwards.
The fundamental building blocks are the regular expres
sions that match a single character. Most characters,
including all letters and digits, are regular expressions
that match themselves. Any metacharacter with special
meaning may be quoted by preceding it with a backslash.
A list of characters enclosed by [ and ] matches any sin
gle character in that list; if the first character of the
list is the caret ^ then it matches any character not in
the list. For example, the regular expression
[0123456789] matches any single digit. A range of charac
ters may be specified by giving the first and last charac
ters, separated by a hyphen. Finally, certain named
classes of characters are predefined. Their names are
self explanatory, and they are [:alnum:], [:alpha:],
[:cntrl:], [:digit:], [:graph:], [:lower:], [:print:],
[:punct:], [:space:], [:upper:], and [:xdigit:]. For
example, [[:alnum:]] means [0-9A-Za-z], except the latter
form depends upon the POSIX locale and the ASCII character
encoding, whereas the former is independent of locale and
character set. (Note that the brackets in these class
names are part of the symbolic names, and must be included
in addition to the brackets delimiting the bracket list.)
Most metacharacters lose their special meaning inside
lists. To include a literal ] place it first in the list.
Similarly, to include a literal ^ place it anywhere but
first. Finally, to include a literal - place it last.
The period . matches any single character. The symbol \w
is a synonym for [[:alnum:]] and \W is a synonym for
[^[:alnum]].
The caret ^ and the dollar sign $ are metacharacters that
respectively match the empty string at the beginning and
end of a line. The symbols \< and \> respectively match
the empty string at the beginning and end of a word. The
symbol \b matches the empty string at the edge of a word,
and \B matches the empty string provided it's not at the
edge of a word.
A regular expression may be followed by one of several
repetition operators:
? The preceding item is optional and matched at most
once.
times.
+ The preceding item will be matched one or more
times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but
not more than m times.
Two regular expressions may be concatenated; the resulting
regular expression matches any string formed by concate
nating two substrings that respectively match the concate
nated subexpressions.
Two regular expressions may be joined by the infix opera
tor |; the resulting regular expression matches any string
matching either subexpression.
Repetition takes precedence over concatenation, which in
turn takes precedence over alternation. A whole subex
pression may be enclosed in parentheses to override these
precedence rules.
The backreference \n, where n is a single digit, matches
the substring previously matched by the nth parenthesized
subexpression of the regular expression.
In basic regular expressions the metacharacters ?, +, {,
|, (, and ) lose their special meaning; instead use the
backslashed versions \?, \+, \{, \|, \(, and \).
Traditional egrep did not support the { metacharacter, and
some egrep implementations support \{ instead, so portable
scripts should avoid { in egrep patterns and should use
[{] to match a literal {.
GNU egrep attempts to support traditional usage by assum
ing that { is not special if it would be the start of an
invalid interval specification. For example, the shell
command egrep '{1' searches for the two-character string
{1 instead of reporting a syntax error in the regular
expression. POSIX.2 allows this behavior as an extension,
but portable scripts should avoid it.
ENVIRONMENT VARIABLES
GREP_OPTIONS
This variable specifies default options to be
placed in front of any explicit options. For exam
ple, if GREP_OPTIONS is '--binary-files=without-
match --directories=skip', grep behaves as if the
two options --binary-files=without-match and
--directories=skip had been specified before any
explicit options. Option specifications are sepa
rated by whitespace. A backslash escapes the next
containing whitespace or a backslash.
LC_ALL, LC_MESSAGES, LANG
These variables specify the LC_MESSAGES locale,
which determines the language that grep uses for
messages. The locale is determined by the first of
these variables that is set. American English is
used if none of these environment variables are
set, or if the message catalog is not installed, or
if grep was not compiled with national language
support (NLS).
LC_ALL, LC_CTYPE, LANG
These variables specify the LC_CTYPE locale, which
determines the type of characters, e.g., which
characters are whitespace. The locale is deter
mined by the first of these variables that is set.
The POSIX locale is used if none of these environ
ment variables are set, or if the locale catalog is
not installed, or if grep was not compiled with
national language support (NLS).
POSIXLY_CORRECT
If set, grep behaves as POSIX.2 requires; other
wise, grep behaves more like other GNU programs.
POSIX.2 requires that options that follow file
names must be treated as file names; by default,
such options are permuted to the front of the
operand list and are treated as options. Also,
POSIX.2 requires that unrecognized options be diag
nosed as "illegal", but since they are not really
against the law the default is to diagnose them as
"invalid". POSIXLY_CORRECT also disables
_N_GNU_nonoption_argv_flags_, described below.
_N_GNU_nonoption_argv_flags_
(Here N is grep's numeric process ID.) If the ith
character of this environment variable's value is
1, do not consider the ith operand of grep to be an
option, even if it appears to be one. A shell can
put this variable in the environment for each com
mand it runs, specifying which operands are the
results of file name wildcard expansion and there
fore should not be treated as options. This behav
ior is available only with the GNU C library, and
only when POSIXLY_CORRECT is not set.
DIAGNOSTICS
Normally, exit status is 0 if matches were found, and 1 if
no matches were found. (The -v option inverts the sense
of the exit status.) Exit status is 2 if there were syn
tax errors in the pattern, inaccessible input files, or
other system errors.
Email bug reports to bug-gnu-utils@gnu.org. Be sure to
include the word "grep" somewhere in the "Subject:" field.
Large repetition counts in the {m,n} construct may cause
grep to use lots of memory. In addition, certain other
obscure regular expressions require exponential time and
space, and may cause grep to run out of memory.
Backreferences are very slow, and may require exponential
time.
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